TIF_NOHZ can escape nonhz mask? (Was: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases)

From: Oleg Nesterov
Date: Mon Jul 28 2014 - 15:00:38 EST

Off-topic, but...

On 07/28, Oleg Nesterov wrote:
> But we should always call user_exit() unconditionally?

Frederic, don't we need the patch below? In fact clear_() can be moved
under "if ()" too. and probably copy_process() should clear this flag...

Or. __context_tracking_task_switch() can simply do

if (context_tracking_cpu_is_enabled())
set_tsk_thread_flag(next, TIF_NOHZ);
clear_tsk_thread_flag(next, TIF_NOHZ);

and then we can forget about copy_process(). Or I am totally confused?

I am also wondering if we can extend user_return_notifier to handle
enter/exit and kill TIF_NOHZ.


--- x/kernel/context_tracking.c
+++ x/kernel/context_tracking.c
@@ -202,7 +202,8 @@ void __context_tracking_task_switch(stru
struct task_struct *next)
clear_tsk_thread_flag(prev, TIF_NOHZ);
- set_tsk_thread_flag(next, TIF_NOHZ);
+ if (context_tracking_cpu_is_enabled())
+ set_tsk_thread_flag(next, TIF_NOHZ);


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